The present invention relates to a telephone system with which a connection can be provided between two subscribers, at least the telephone of one of them being a portable low-powered radio telephone.
The paging system is a widely employed system in which using a rather powerful signal emitted from a fixed paging exchange a person possessing a radio pager is alerted and a short message, ordinarily a call request or a telephone number, is stored in the pager memory. The person may then dial that number using either a wire-connected telephone of the public switching network or a mobile telephone. The paging service is typically regional, based on various media designs operating in the USW (Ultra Short Wave) band or with the base stations. The essential feature of the system is that the message transmission is one-way, from the exchange to the paging device. The pager is thus a small receiver in which the current consumption can be kept minimal. The power supply may be spared by switching the receiver on only periodically, provided that the messages in the transmission system concerning a given pager are transmitted at regular intervals.
In the cellular radiotelephone system of prior art the transmission of message is bidirectional and therefore, a connection has to be set up between the A subscriber and the B subscriber. In the traditional cellular system the exchange, or base station, is all the time informed of the location of all those telephones to which a call can be directed. When the system covers a wide area, this is an efficient way. If a mobile travel telephone frequently gets out of the reception range of the base stations, or moves frequently from one area of the base station to another, as the case is in a small cellular network, the reporting obligation of the telephones becomes a considerable load on the network, and this requires a quite high cost computer network in the system. In this kind of system the telephone must also be switched on continuously, which of course is power consuming.
Such systems are also known in the art in which the telephones are not continuously registered; instead, they are registered only when a call is made from the mobile telephone. In such a system incoming calls cannot usually be directed to the mobile telephone. For instance, the so-called Telepoint system is a system of this kind, in which so-called cordless telephone are used, from which a call can be made at a certain distance, e.g. 100 m, from any fixed station. The telephones are lightweight and small in size, fitting in a pocket, but it is usually not possible with this telephone to receive a call anywhere but within the area of a specified home base station.
In the EP patent application No. 0212761, a system is disclosed in which a cordless telephone and a paging device system are combined, making use as extensively as possible of existing systems, whereby remarkable expenditure savings are achieved. Said system comprises a paging network which can be accessed from the public telephone network, and a number of fixed, geographically spread, stations connected to the public switching network and containing a transmitter/receiver, and a number of cordless telephones which may through a fixed station enter connection with the public network. The power of the cordless telephones is 10 mW. The cordless telephone is provided with a pager to which a message, ordinarily a telephone number, can be transmitted via a paging network. The pager is provided with a memory in which a plurality of paging messages can be stored. When making a call from a cordless telephone to a telephone in the public switching network, the caller goes to the neighbourhood of a fixed station, and, if necessary, tunes to the frequency thereof and makes the call in the normal way. When a subscriber of the public telephone network calls a cordless telephone, he dials the paging number of this telephone (which at the same time is the address number of the telephone), hangs-up his telephone and waits. The paging exchange transmits through the transmitters of the paging stations the number of the cordless telephone and the subscriber's telephone number to all paging receivers. The pager of the particular cordless telephone then alerts and the subscriber's telephone shows up in the display. The user of the cordless telephone will now approach the nearest unoccupied fixed station and call the number of the subscriber. This may also take place automatically in that the cordless telephone automatically transmits the number of the calling subscriber if the telephone is within the range of a fixed station. When a call is made from one cordless telephone to another, the A subscriber dials in the vicinity of a fixed station the number of the B subscriber. The station adds thereto its own identification and transmits the numbers to the exchange of the public network which in turn transmits them to the paging exchange, which thereupon transmits the numbers via the paging stations to all paging receivers. The respective device alerts and the B subscriber calls the number of the A subscriber shown in the display. For the connection to be successful, the A subscriber must during this time be within the range of that station where he initiated the call, and remain connected to it because the response call of the B subscriber will be routed to this particular station.
The system disclosed in the EP patent application No. 0212761 cited above is encountered by a number of shortcomings, such as the following:
The paging exchange transmits the paging message through the paging stations simultaneously throughout its network because the location of the telephone is not known. The fixed station, that is, the base station has only one channel which must be maintained engaged for location detection when calling from one telephone to another. The paging messages are stored in the paging receiver, which results in losing the message if the paging receiver is not switched on or if it is outside the search range. When the incoming call cannot be put through the system, the call is replaced with an automatically dialed response call. A call between two mobiles implies that the calling telephone is locked on to the fixed station from which the call was initiated. Therefore, the mobility is limited to the immediate vicinity of said fixed station.